A number of binary heat transfer fluids are known. The eutectic mixture of diphenyl oxide and biphenyl is widely used as a desirable heat transfer fluid. This fluid has a freezing point of 54.degree.F. The components of the binary fluids of the invention are known. Some of these components have been employed in heat transfer fluids prior to the present invention, see for example Giolito et al. in U.S. Pat. No. 3,429,816, Fields at al. in U.S. Pat. No. 3,109,868 and Ritler et al. in U.S. Pat. No. 2,149,789.
None of these references, however, suggests the combinations of the present invention, nor their broad range of liquidity without significant sacrifice of high temperature thermal stability.